1. Field of the Invention
The present invention relates to a semiconductor laser module, an optical measuring method and an optical measuring apparatus, and more particularly, to a semiconductor laser module for emitting laser light with the center wavelength in a range of 1300 to 1440 nm, and an optical measuring method and an optical measuring apparatus for measuring characteristics of laser light with the center wavelength in a range of 1300 to 1440 nm.
2. Description of the Related Art
In recent years, with the establishment of Raman amplification technology, a Raman amplifier which uses a pumping light source which emits a laser light at wavelength of around 1400 nm has entered into practice. The Raman amplifier employs a semiconductor laser module (hereinafter called the “LD module”) as a pumping light source, which has a semiconductor laser device (hereinafter called the “LD device”) encapsulated in a package.
However, it has been found that when laser light, for example, in a wavelength band of 1300 to 1440 nm is output from an LD module, a difference exists in the stability of laser oscillation depending on the center wavelength. For example, in a relationship between a driving current value and a quantum efficiency (derived by differentiating the light power of the LD device by the driving current value) representing the stability of oscillating state of the laser light from the LD device, kinks were found on a characteristic curve representing the relationship. Here, the term “kink” is a nonlinear portion which does not change continuously. In this way, the laser light from the LD module exhibited unstable characteristics in some cases.
It has been also revealed that measurements of laser light in a wavelength band of 1300 to 1440 nm may provide different results depending on the center wavelength. For example, in some cases, kinks were found on a characteristic curve representative of the quantum efficiency characteristic. In this way, the optical characteristics of laser light are not precisely measured at all times.